Signaling mechanism for modem connection holding and reconnecting

ABSTRACT

A quick startup procedure for a modem system utilizes known characteristics of a previously established communication channel to reduce the initialization period associated with subsequent connections over the same channel. In response to the establishment of a call, the modem devices determine whether the quick connect protocol is supported. If so, then the called modem transmits a modified answer tone to the calling modem. The calling modem analyzes the signal received in response to the modified answer tone to determine whether characteristics of the current channel are similar to stored characteristics associated with a previous connection over the same channel. If a channel “match” is found, then the modem devices carry out a quick initialization routine that eliminates, abbreviates, or modifies a number of procedures or protocols that are carried out in conventional modem startup processes. The general quick startup techniques may also be applied in the context of a quick reconnect procedure that can be performed in response to a temporary pausing or disconnecting of the data modem mode.

RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. provisional application serial No. 60/128,874, filed Apr. 12, 1999. This application is a Continuation-In-Part of U.S. application Ser. No. 09/394,018, filed Sep. 10, 1999, which is a Continuation-In-Part of U.S. application Ser. No. 09/361,842, filed Jul. 27, 1999.

FIELD OF THE INVENTION

[0002] The present invention relates generally to modem systems. More particularly, the present invention relates to the initialization and reconnection of a V.90 modem system.

BACKGROUND OF THE INVENTION

[0003] 56 kbps modems are now standardized in accordance with the ITU V.90 Recommendation. However, many 56 kbps modems, particularly end user modems, may only be compatible with legacy modes such as K56flex, V.34, V.FC, and V.32. Such legacy modems, and downwardly compatible V.90 modems, may have an undesirably long connect or initialization time between dial-up and full rate data mode. The startup time can be up to 30 seconds, which can be rather annoying and unattractive from the perspective of the end user, especially in light of other data communication protocols that appear to operate in an “always connected” manner.

[0004] V.90 modems that support legacy modem protocols typically perform the functions shown in Table 1 during initialization. The time periods associated with the operations set forth in Table 1 may vary from connection to connection depending upon various factors such as the server speed and channel conditions. TABLE 1 Conventional V.90 Modem Startup PROTOCOL OPERATION TIME (seconds) — Dialing 1 — Call Establishment 1 V.8 bis Capabilities Exchange 3.5 V.8 Capabilities Exchange 3.5 V.90 Phase 2 Probing & Ranging 1.5 V.90 Phase 3 Digital Impairment Learning; 8.5 Initial APCM Training V.90 Phase 4 Final APCM Training; 2.5 Set Power Levels; Constellation Transmission V.42/V.42 bis Error Correction; 0.5 Data Compression — Login 0.5-5 TOTAL = 22.5-27.0

[0005] The V.8bis operation includes a relatively long timeout period that encompasses much of the time period associated with the operation. This operation is described in detail in ITU-T Recommendation V.8bis (International Telecommunication Union, August 1996), the content of which is incorporated by reference herein. The V.8bis protocol is an extension of the V.8 protocol, as described in ITU-T Recommendation V.8 (International Telecommunication Union, February 1998), the content of which is incorporated by reference herein. In accordance with V.8bis and/or V.8, the two modem devices exchange their individual capabilities such that compatible protocols may be utilized during subsequent initialization and data communication procedures.

[0006] The various V.90 startup phases are utilized to determine the analog and digital channel characteristics, to train the modem equalizers, and to otherwise attempt to optimize the current communication session. The details of the V.90 startup phases and other aspects of a V.90 modem system may be found in ITU-T Recommendation V.90 (International Telecommunication Union, September 1998), the content of which is incorporated by reference herein. Although a portion of the V.90 startup segments shown in Table 1 are required without regard to the location or status of the client modem, many of the operations could be eliminated or shortened upon repeated connections associated with the same (or nearly identical) channel characteristics.

[0007] In a conventional V.90 modem system, error correction and data compression techniques are performed during the V.42/V.42bis stage. The specifics of V.42 are contained in ITU-T Recommendation V.42 (International Telecommunication Union, October 1996), the content of which is incorporated by reference herein. The specifics of V.42bis are contained in ITU-T Recommendation V.42bis (International Telecommunication Union, January 1990), the content of which is incorporated by reference herein. The V.42 operation is desirable such that the modem system can perform the login procedure in a substantially “error free” mode. The login procedure may be conducted with CHAP and PAP protocols; both are utilized for security purposes in the context of point-to-point protocol (“PPP”) connections, e.g., a connection between a client computer and an internet service provider server. From the perspective of the V.90 modem devices, the login information is transmitted as data. Once the login procedure is performed, the dial-up connection is complete and data may be transmitted between the server and the host software associated with the client.

[0008] The widespread use of the internet as a daily research, entertainment, and communication tool has increased the deployment of 56 kbps modems. However, many channels can only support legacy modes such as V.34. Thus, although most newer modems (particularly those sold with new personal computers) are compatible with the V.90 Recommendation, many legacy modes are still in use. The long initialization period associated with V.90 modems that fall back into legacy modes may be annoying and undesirable in many applications and can be a serious hindrance where a user would like to establish an immediate connection after an unanticipated disconnect. In addition, even in the context of a connection between two V.90 modem devices, the long V.90 startup phases may test the mettle of an impatient end user. Accordingly, it would be highly desirable to reduce the initialization time normally associated with a conventional V.90 modem system.

[0009] A given modem communication session may be interrupted or disconnected for any number of reasons. For example, a call waiting signal may disrupt a modem connection to the extent that the modem call must either be reconnected or reinitialized. As another example, it may be possible to place a current modem connection on hold to enable the user to answer an incoming call in response to a call waiting signal or to enable the user to place an outgoing call without disconnecting the modem connection. Ideally, the modem connection could be re-established in an instantaneous manner. However, in a practical system, a retraining or reinitialization procedure must be carried out to ensure that the two end devices are properly synchronized and to ensure that the channel is adequately equalized. As discussed above, conventional V.90 modem systems may spend more than 20 seconds during such retraining and reinitialization. Accordingly, it would also be desirable to reduce the reconnection time between the same modem devices in response to a temporary disconnect or a temporary pause in the data communication.

SUMMARY OF THE INVENTION

[0010] The present invention provides techniques to shorten the startup and reconnection times associated with a data communication system that employs a modem. The quick reconnect technique leverages the known channel characteristics of a previous connection to reduce the reinitialization period associated with subsequent attempts to reconnect the same two modem devices. In accordance with one illustrative embodiment, the techniques of the present invention are utilized to reduce the reconnection time for a communication session that follows an upper layer protocol, e.g., PPP. Although not limited to any specific modem application, the quick startup and reconnect procedures may be used to eliminate portions of the initialization protocols or processes normally employed by a V.90 modem, e.g., V.8bis, V.8, digital impairment learning, initial training, probing and ranging, or the like. In addition, the quick startup and reconnect techniques may perform certain operations at a different time or in a different order in comparison to a conventional modem startup technique.

[0011] The above and other aspects of the present invention may be carried out in one form by a method for reducing the reconnection time associated with a data transmission system having a first device configured to communicate with a second device over a communication channel. The illustrative method involves establishing a communication session between the first device and the second device over the communication channel, obtaining a number of operating parameters for the data transmission system, where the operating parameters are associated with the communication channel, and storing at least one of the operating parameters at the second device. After a temporary pause in the communication session, the operating parameters are recalled at the second device.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] A more complete understanding of the present invention may be derived by referring to the detailed description and claims when considered in connection with the Figures, where like reference numbers refer to similar elements throughout the Figures, and:

[0013]FIG. 1 is a block diagram depicting a general modem system environment capable of supporting point-to-point protocol (“PPP”) connections;

[0014]FIG. 2 is a flow diagram of a general quick startup process according to the present invention;

[0015]FIG. 3 is a block diagram depicting an illustrative modem system configured in accordance with the present invention;

[0016]FIG. 4 is a flow diagram illustrating portions of a quick startup process performed by two modem devices;

[0017]FIG. 5 is a timing diagram corresponding to a quick startup process performed by two modem devices;

[0018]FIG. 6 is a timing diagram corresponding to a quick reconnect process performed by two modem devices;

[0019]FIG. 7 is a flow diagram illustrating a quick reconnect process performed by two modem devices;

[0020] FIGS. 8-15 are timing diagrams corresponding to different modem-on-hold, reconnect, and clear down situations; and

[0021]FIG. 16 is a block diagram of a modem system environment in which various aspects of the present invention may be incorporated.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

[0022] The present invention may be described herein in terms of functional block components and various processing steps. It should be appreciated that such functional blocks may be realized by any number of hardware components configured to perform the specified functions. For example, the present invention may employ various integrated circuit components, e.g., memory elements, digital signal processing elements, logic elements, look-up tables, and the like, which may carry out a variety of functions under the control of one or more microprocessors or other control devices. In addition, those skilled in the art will appreciate that the present invention may be practiced in any number of data communication contexts and that the modem system described herein is merely one illustrative application for the invention. Further, it should be noted that the present invention may employ any number of conventional techniques for data transmission, signaling, signal processing and conditioning, and the like. Such general techniques that may be known to those skilled in the art are not described in detail herein.

[0023] It should be appreciated that the particular implementations shown and described herein are merely exemplary and are not intended to limit the scope of the present invention in any way. Indeed, for the sake of brevity, conventional encoding and decoding, timing recovery, automatic gain control (“AGC”), synchronization, training, and other functional aspects of the data communication system (and components of the individual operating components of the system) may not be described in detail herein. Furthermore, the connecting lines shown in the various figures contained herein are intended to represent exemplary functional relationships and/or physical couplings between the various elements. It should be noted that many alternative or additional functional relationships or physical connections may be present in a practical communication system.

[0024]FIG. 1 is a block diagram depicting a general modem system 100 in which the techniques of the present invention may be practiced. For purposes of this description, modem system 100 is assumed to be capable of supporting connections associated with an upper layer protocol, e.g., point-to-point protocol (“PPP”) connections. PPP connections are typically associated with internet communications between, e.g., an individual end user and an internet service provider. In this respect, modem system 100 includes a plurality of server modems (identified by reference numbers 102 a, 102 b, and 102 n) and a client modem 104. Server modems 102 may each be associated with an internet service provider or any suitable data source. Client modem 104 may be associated with a suitable data source, e.g., a personal computer capable of running host software 105. For purposes of this description, host software 105 may be an operating system such as MICROSOFT WINDOWS, or any application program capable of functioning in conjunction with modem system 100. Although not shown in FIG. 1, client modem 104 may be integrated with the personal computer.

[0025] In the context of this description, modem system 100 may employ 56 kbps modems that are compatible with the V.90 Recommendation, legacy 56 kbps protocols, the V.34 Recommendation, or the like. Although the present invention is described herein in the context of a V.90 modem system, the techniques can be equivalently applied in a V.34 modem system or in any number of legacy modem systems. V.90 or 56 kbps modem devices are suitable for use in modem system 100 where a given server modem 102 utilizes a digital connection 106 to the digital telephone network 108. The client modem 104 is connected to a local central office 110 via an analog local loop 112. Thus, the communication channel established between client modem 104 and any server modem 102 is digital up to the central office 110. Thereafter, the digital signals are converted to an analog signal for transmission over the local loop 112.

[0026] If an end user desires to establish an internet connection, host software 105 may perform any number of operations in response to a user command. For example, host software 105 may prompt client modem 104 to dial the telephone number associated with server modem 102 a (which, for this example, is the server modem associated with the user's internet service provider). Server modem 102 a and client modem 104 perform a handshaking routine that initializes the equalizers, echo cancelers, transmit power levels, data rate, and possibly other operational parameters associated with the current communication channel. In addition, host software 105 may cause client modem 104 to transmit and receive authentication data that enables the user to log onto the internet via the service provider. As mentioned above, the authentication data may be exchanged between server modem 102 a and client modem 104 in accordance with the known CHAP or PAP techniques. In an alternate embodiment that employs a non-PPP upper layer protocol, a suitable login procedure may be conducted instead of the CHAP or PAP procedures.

[0027] As discussed previously, the dial-up connection time (and reconnection time) associated with conventional modem systems may be undesirably long. The present invention takes advantage of the repeated use of a communication channel between modem devices, e.g., the communication channel that is established between server modem 102 a and client modem 104. Assuming that client modem 104 is associated with a desktop personal computer resident at a specific location, the connection to any given server modem 102 will necessarily be established over the same analog communication channel. In other words, client modem 104 will always establish an analog channel between the user premises and central office 110. Disregarding slight variations in the analog channel due to temperature and other environmental effects, the initialization of client modem 104 (with respect to the analog channel) will remain substantially constant from connection to connection.

[0028]FIG. 2 is a flow diagram of a general quick startup process 200 that may be performed by a data communication system such as modem system 100. In a practical system, process 200 may be cooperatively performed by server modem 102, client modem 104, host software 105, and/or any functional component of modem system 100. In addition, process 200 may be realized in the context of an overall initialization procedure that follows any number of conventional modem protocols.

[0029] Quick startup process 200 may begin with a task 202, which relates to the establishment of a call between client modem 104 and a server modem 102. In the context of this example, client modem 104 is considered to be the calling device. Accordingly, host software 105 and/or client modem 104 dials the telephone number associated with, e.g., server modem 102 b. Assuming that server modem 102 b is capable of making an additional connection, it will go off hook and generate a suitable answer tone in a conventional manner. When both modem devices are off hook and communicating with each other, a communication channel is established via digital connection 106, telephone network 108, central office 110, and analog local loop 112. The dialing, ringing, and answering procedures utilized during task 202 may follow conventional protocols.

[0030] Following task 202, a query task 204 may be performed by modem system 100 to ascertain whether a quick connect protocol is supported. Query task 204 may be necessary to enable different server modems and different client modems to be interoperable and compatible. For example, server modem 102 b may be a V.90 modem device that supports the quick connect features of the present invention, while client modem 104 may be a legacy 56 kbps modem device that does not support the quick connect features. Portions of query task 204 may be performed by server modem 102 b or client modem 104. An illustrative technique for performing query task 204 is described in detail below. Task 204 may be equivalently performed when client modem 104 initiates the call or when server modem 102 initiates the call.

[0031] If query task 204 determines that the quick connect protocol is not supported by both modem devices, then a task 206 may follow. Task 206 prompts modem system 100 to begin a conventional initialization routine. For example, in the context of a V.34 or V.90 modem system, task 206 may begin a capabilities exchange protocol such as V.8bis. Alternatively, some modem systems may only implement the V.8 capabilities exchange protocol. Older legacy modem systems may skip the V.8 and V.8bis procedures altogether and perform an appropriate initialization routine according to the legacy mode. Following task 206, modem system 100 may conduct a known startup procedure in accordance with an applicable modem specification. For example, if modem system 100 supports V.90, then task 208 may be associated with conventional V.90 equalizer training, echo canceler training, constellation design, power level verification, and other startup operations. If tasks 206 and 208 are performed, then the startup time associated with the communication session is essentially the same as the startup time for a conventional V.90 connection.

[0032] If query task 204 determines that the quick connect protocol is fully supported, then a query task 210 may also be performed. Query task 210 tests whether the characteristics of the established communication channel are similar to corresponding characteristics of a previously established communication channel. Briefly, query task 210 compares one or more attributes of a received sequence to stored attributes of a previously received sequence associated with the previously established channel. The received signal conveys information regarding the characteristics of the communication channel. In particular, the received signal conveys information relative to analog local loop 112.

[0033] In the illustrative embodiment described herein, where one modem device is connected digitally to the digital telephone network 108, analog local loop 112 affects signals in a substantially consistent manner from connection to connection. Although the analog characteristics will be similar for repeated connections to the same server modem 102, slight variations in temperature, humidity, other environmental changes, physical changes in the system hardware, and other operational parameters contribute to random fluctuations in the current channel characteristics used for comparison purposes. Nonetheless, the comparison procedure performed during query task 210 is preferably designed to accommodate such fluctuations. For purposes of this description, “similar” characteristics means that query task 210 will assume that the current channel matches a previous channel notwithstanding normal variations due to the uncontrollable and unpredictable factors mentioned above.

[0034] If query task 210 determines that the parameters of the current communication channel do not match the parameters of a previous communication channel, then a task 212 may be performed. Task 212, like task 206, prompts modem system 100 to begin a conventional initialization routine. In a preferred embodiment, if modem system 100 verifies that the quick connect protocol is fully supported (query task 204), then most, if not all, of the V.8bis procedure may be skipped. Accordingly, the V.8 capabilities exchange protocol may be prompted by task 212. Thereafter, a task 214 may be performed to cause modem system 100 to enter the conventional V.90 startup procedure. Task 214 is similar to task 208 described above. If tasks 212 and 214 are performed, then the startup time associated with the communication session may be reduced by approximately three seconds, which is the typical time period required to conduct the V.8bis procedures. Accordingly, even if query task 210 determines that the current channel is not similar to a previous channel, quick startup process 200 reduces the overall initialization time of modem system 100.

[0035] If query task 210 finds that the current channel characteristics “match” the stored characteristics of a previously established channel, then a task 216 may be performed. An abbreviated training procedure is conducted during task 216. As described in more detail below, modem system 100 leverages the known characteristics of the current channel such that the modem devices can be immediately trained. For example, although the specific timing phase of digital impairments (e.g., robbed bit signaling) may be unknown, the types of digital impairments will be consistent for repeated connections. Thus, in the context of a V.90 modem system, the lengthy digital impairment leaning procedure need not be fully implemented. In addition, the initial training of equalizers and echo cancelers, and the initial determination of PCM codec transmit levels and data rates need not be performed.

[0036] A task 218 may be performed to enable modem system 100 to operate at an initial data rate. It should be appreciated that portions of the training associated with task 216 may be performed at the initial data rate associated with task 218. Modem system 100 is able to quickly operate at the initial data rate by recalling the initialization parameters associated with the previously stored channel. During task 218, modem system 100 may perform final training of the equalizers and echo cancelers, exchange modulation parameters, and exchange constellation signal points for use during the full rate data mode. In accordance with the present invention, PPP data may be transmitted during task 218 in connection with one or more final training sequences. For example, the PPP data may be associated with the exchange of log-in authentication information, e.g., CHAP or PAP information. In view of the transmission of data during task 218, this portion of quick startup process 200 may be considered to be a first data mode or a data phase one.

[0037] Following task 218, quick startup process 200 causes modem system 100 to operate at a final data rate (task 220). In the context of this embodiment, this portion of process 200 may be considered to be a second data mode or a data phase two. The transition between the initial and final data rates preferably occurs in a seamless manner; modem system 100 employs a suitable signal timing or synchronization technique to enable such a data rate transition. During the full data mode, modem system 100 utilizes the signal point constellation exchanged during task 218. Once modem system enters the final data mode, quick startup process 200 ends.

[0038]FIG. 3 is a block diagram depicting an illustrative modem system 300 configured in accordance with the present invention. Modem system 300 is preferably configured to carry out quick startup process 200 and other processes described herein. By way of example, modem system 300 is described herein in the context of a 56 kbps or V.90 system (or a system substantially similar to a V.90 system). However, it should be appreciated that the particular implementation shown in FIG. 3 is not intended to limit the scope of the present invention in any way.

[0039] Generally, modem system 300 includes a first modem, e.g., modem 302, and a second modem, e.g., modem 304. In the context of this description, modem 302 is considered to be a server modem and modem 304 is considered to be a client modem (see FIG. 1). It should be appreciated that modems 302 and 304 may be similarly configured such that both can function in either a transmit or receive mode. Modems 302 and 304 are generally configured in accordance with known principles to communicate over a telecommunication network, such as the public switched telephone network (“PSTN”) 306, via at least one communication channel (e.g., channels 308 and 310). For purposes of this description, modem 302 is connected digitally to PSTN 306 while modem 304 is connected to PSTN via a central office (not shown) and an analog local loop, as described above in connection with FIG. 1. For the sake of clarity, FIG. 3 does not show the various encoder, decoder, and other functional elements that would typically be present in a practical modem system.

[0040] Modem 302 may include a processor element 312, while modem 304 may include a processor element 314. In addition to the specific operations described herein, processors 312 and 314 are suitably configured to carry out various tasks associated with the operation of modem system 300. Indeed, modem system 300 may incorporate any number of processors, control elements, and memory elements as necessary to support its functionality. Such processor, control, and memory elements may suitably interact with other functional components of modems 302 and 304 to thereby access and manipulate data or monitor and regulate the operation of modem system 300.

[0041] Processor 312 may be operatively associated with a quick connect confirmation routine, which is illustrated as a functional block 322. Quick connect confirmation routine 322 may be employed during query task 204 (see FIG. 2). Processor 312 is also operatively associated with a number of training routines 324. Training routines 324 may be utilized for initial and/or final training of modem system 300. Training routines 324 may be employed during task 216, as described above. Processor 312 may also operate in conjunction with a dial-up authentication scheme 326, e.g., information exchanging in accordance with PAP or CHAP. The CHAP/PAP functionality may be alternatively (or additionally) realized in one or more software applications maintained by the server corresponding to modem 302. These illustrative operations are not intended to limit the applicability of processing element 312, which is preferably configured to support any number of additional operations.

[0042] Modem 302 includes a transmitter 316, which is configured to transmit encoded symbols in accordance with conventional data transmission techniques. Such symbols may represent data, training sequences, synchronization signals, control signals, information exchange sequences, and any suitable communication signal utilized by modem system 300. Modem 302 also includes a receiver 318, which may be configured in accordance with any number of known modem technologies. Receiver 318 is configured to receive communication signals from modem 304; such signals may include encoded information bits, control signals, information exchange sequences, training sequences, and the like. Receiver 318 may include or be functionally associated with an equalizer structure 317 and an echo canceler structure 319. The configuration and operation of equalizer structure 317 and echo canceler structure 319 may be consistent with any number of conventional techniques, e.g., adaptive filtering algorithms.

[0043] Modem 302 is preferably configured to generate, process, and transmit different data and signals associated with the operation of modem system 300. Such data, signals, and sequences may be suitably stored, formatted, and produced by any number of microprocessor-controlled components. For illustrative purposes, FIG. 3 depicts a number of blocks related to different operational features of modem system 300; such operational features may have specific data sequences, control signals, or the like, associated therewith. Although a practical system may process and transmit any amount of additional or alternative data, the particular embodiment described herein functions in cooperation with at least the following types of data: a transition sequence 328, an answer signal point sequence 330, authentication information 332, a quick connect identifier 334, training information 336, and user data 338. This data, and the handling of the data by modem system 300, is described in detail below.

[0044] Modem 302 also includes a suitable amount of memory 320 necessary to support its operation. Memory element 320 may be a random access memory, a read only memory, or a combination thereof. Memory element 320 may be configured to store information utilized by modem system 300 in connection with one or more processes related to the present invention. For example, memory element 320 may be configured to store a suitable answer signal point sequence 338. Memory 320 may store specific signal points, transmit levels, a pattern utilized to format a sequence for transmission, or the like. In the preferred embodiment, answer signal point sequence 338 corresponds to sequence 330 (described above). Memory element 320 may also be configured to store a number of parameters related to the training of receiver 318. These receiver parameters, which are depicted as block 340, may be associated with the initialization of equalizer structure 317 and/or echo canceler structure 319. As a practical matter, memory element 320 may store information related to the analog and/or digital characteristics, e.g., filter tap coefficients, of equalizer structure 317 and echo canceler structure 319, and transmit codec level estimates.

[0045] In accordance with a preferred embodiment of the present invention, memory element 320 is also capable of storing a number of parameters, attributes, and/or characteristics of a previously established channel (illustrated as a previous channel block 342). The previous channel parameters 342 may be stored at any suitable time during a communication session or periodically updated during a session. Indeed, modem 302 and modem 304 may both be configured to save the current channel parameters to anticipate a temporary interruption, delay, or disconnection associated with the current communication session (whether such interruption, delay, or disconnection is intentional or unintentional). As described in more detail below, in response to a temporary disconnection or pause in the modem data transmission mode, modem 302 can be placed “on hold” until the communication session is to be reinitiated. At that time, modems 302 and 304 may access the stored channel parameters rather than conduct a lengthy retrain procedure.

[0046] Modem 304 includes a receiver 350, which is operatively associated with an equalizer structure 352 and an echo canceler structure 354. Receiver 350 is configured to receive communication signals from modem 302. Modem 304 also includes a transmitter 356 configured to transmit communication signals to modem 302. These components of modem 304 may be similar to the corresponding components of modem 302. Thus, for the sake of brevity, the description of features and functions that are common to modems 302 and 304 will not be repeated in this description of modem 304.

[0047] Processor 314 may be operatively associated with a quick connect confirmation routine 358, one or more training routines 360, and a dial-up authentication scheme 362. These processing functions are similar to the corresponding functions described above in connection with processor 312. In addition to these features, processor 314 may be operatively associated with a digital impairment learning routine 364. Digital impairment learning routine 364 may be compatible with the digital impairment learning procedure carried out by conventional V.90 modems. Routine 364 may be utilized to enable modem 304 to analyze a digital impairment learning sequence transmitted by modem 302 and to determine the types of digital impairments present in the communication channel and any timing phases associated with such digital impairments. Routine 364 may interact with a memory element 366 such that modem 304 can store the digital impairment profile associated with a given communication channel. Routine 364 may enable modem 304 to select appropriate signal points (or a signal point) that function to illuminate or highlight robbed bit signaling present in the channel. For example, if modem 304 determines that the network forces robbed bits (typically the least significant bit of a symbol) to zeros, then a signal point having a least significant bit of one may be selected such that the robbed bit signaling phases can be easily detected.

[0048] Processor 314 may also be configured to conduct a channel comparison routine 368, which may be performed during task 210 described above in connection with FIG. 2. Channel comparison routine 368 preferably determines whether the characteristics of the current communication channel are similar to stored characteristics associated with a previously established communication channel. In the context of this description, the current channel is a repeated connection of the previously established channel, and a number of stored characteristics may be resident in memory element 366. Routine 368 is described in more detail below.

[0049] As with processor 312, the illustrative operations set forth herein are not intended to limit the applicability of processing element 314, which is preferably configured to support any number of additional operations.

[0050] Like modem 302, modem 304 is configured to generate, process, and transmit different data and signals associated with the operation of modem system 300. Such data, signals, and sequences may be suitably stored, formatted, and produced by any number of microprocessor-controlled components. Although a practical system may process and transmit any amount of additional or alternative data, transmitter section 356 is illustrated in conjunction with the following types of data: a quick connect identifier 370, a transition sequence signal point identifier 372, training information 374, authentication information 376, and user data 378. This data, and the handling of the data by modem system 300, is described in detail below.

[0051] As mentioned above, modem 304 includes a suitable amount of memory 366 necessary to support its operation. Memory element 366 is similar to memory element 320. In the preferred embodiment, memory element 366 is configured to store an answer signal point sequence 380 that is related to the corresponding answer signal point sequence 338 utilized by modem 302. In this embodiment, the same answer signal point sequence is predetermined and known at both modems 302 and 304. Memory element 366 may also store a number of parameters, attributes, and/or characteristics of a previously established channel (illustrated as a previous channel block 382). The previous channel parameters 382 may be stored at any suitable time during a communication session or periodically updated during a session. Like memory element 320, memory element 366 may also be configured to store a number of parameters 384 related to the training of receiver 350. These stored receiver parameters 384 are preferably accessed by modem 304 to effectively reduce the startup latency typically experienced with conventional V.90 modem systems.

[0052] A number of features of the present invention contribute to the reduction in conventional V.90 modem startup and/or reconnect times, e.g., the elimination or abbreviation of the V.8bis procedure, the elimination or abbreviation of the initial training procedure, and the exchanging of login authentication data earlier in the initialization process (rather than waiting until the full data rate is achieved). In one embodiment, the login authentication data is exchanged while the modem system is in an initially trained mode associated with an intermediate data rate. Any one of these (and other) features of the present invention may be implemented in modem system 300.

[0053]FIG. 4 is a flow diagram illustrating portions of a quick startup process 400 performed by two modem devices, and FIG. 5 is a timing diagram 500 corresponding to an illustrative quick startup process performed by two modem devices. Timing diagram 500 includes acronyms and abbreviations that are often used in the context of V.8, V.8bis, V.34, V.90, and other data communication protocols. The use of such terminology herein is intended to illustrate the concepts of the present invention in the context of one practical embodiment. However, the present invention may be employed in any suitable context, and the specific signals, number of sequences, timing of the sequences, data rates, and interaction between the two modem devices shown in FIG. 5 are not intended to limit the scope of the invention in any way.

[0054] Quick startup process 400 is depicted in a manner that indicates tasks associated with a client modem, e.g., an analog pulse code modulation modem (“APCM”), and a server modem, e.g., a digital pulse code modulation modem (“DPCM”). Similarly, timing diagram 500 shows the general sequencing of signals transmitted by an APCM and a DPCM. In FIG. 5, the arrows between the two major sequences represent responses or interactions between the APCM and the DPCM.

[0055] Quick startup process 400 may begin with a task 402, which causes the APCM to dial the telephone number associated with the DPCM. As described above, the call will be established over local loop 112, central office 110, and digital telephone network 108 (see FIG. 1). In response to the initial ring tone, the DPCM may be placed in an off hook state (task 404), i.e., the DPCM will answer the call. Of course, the APCM and the DPCM may be configured to place, answer, and process calls in accordance with conventional telephony protocols. Following task 404, a task 406 may be performed to initialize a capabilities exchange protocol such as V.8 or V.8bis. In the embodiment described herein, a capabilities request signal (represented by CRe′ in FIG. 5) may be transmitted during task 406. The CRe′ signal may function to inform the APCM that the DPCM supports the quick connect procedure. The CRe′ signal may be a modified version of the conventional V.8bis signaling tones, e.g., the V.8bis tones may be amplitude modulated. Alternatively, the frequency associated with a signaling tone may be jittered in a periodic manner or a low-level wideband signal may be added to a tone. In this manner, legacy modem systems will recognize the CRe′ signal as the normal V.8bis CRe signal.

[0056] In response to the establishment of a call associated with the current communication channel, the APCM may perform a task 408 to suitably transmit a quick connect identifier (QC) to the DPCM. In the practical embodiment described herein, the transmission of the quick connect identifier may be prompted in response to the detection of the CRe′ signal by the APCM. The QC signal is preferably designed such that legacy modems and modems that do not support the quick connect protocol are not adversely affected by the QC signal, i.e., the QC signal should be ignored by non-compatible devices. (If the APCM does not support the quick connect techniques described herein, then it will not generate the QC signal and the startup will proceed in a conventional manner, as described above in connection with FIG. 2). In a preferred embodiment, the QC signal also conveys a signal point identifier that identifies signal points (or one point) for use by the DPCM in a transition sequence (represented by QTS and QTS\ in FIG. 5), where the signal points function to highlight, illuminate, or make apparent the digital impairments present in the communication channel. Thus, the QC signal sequence performs a dual function.

[0057] Assuming that the DPCM also supports the quick connect methodology, it preferably performs a task 410 in response to the reception of the QC signal. In connection with task 410, the DPCM transmits a quick connect acknowledgment (represented by the QCA signal in FIG. 5). As described above in connection with FIG. 2, if the DPCM does not acknowledge the QC signal, or if the APCM somehow fails to receive the QCA signal, then the modem system will proceed with a conventional startup procedure. The format, configuration, and processing of the QC and QCA signals may be carried out by the respective portions of the individual modems, as described above in connection with modem system 300 (see FIG. 3).

[0058] If the DPCM and the APCM both support the quick connect technique, then any number of initialization routines may be eliminated, modified, or abbreviated, depending upon the specific application. For example, in the context of a V.90 compatible modem system, the transmission of the QC signal may inherently indicate that the APCM is V.90 compliant. Similarly, the transmission of the QCA signal may inherently indicate that the DPCM is also V.90 compliant. Consequently, the modem system may eliminate portions or the entirety of the normal capabilities exchange protocol or protocols, such as V.8 and/or V.8bis. This feature by itself can reduce the startup latency by as much as five seconds (for a typical connection).

[0059] It should be appreciated that the quick connect identification and verification scheme described above in connection with task 402 through task 410 can be equivalently applied when the DPCM initiates the call to the APCM. Such a situation may arise when, in response to an initial call or request from the APCM, the DPCM calls the APCM to establish the communication channel. In this situation, the APCM will transmit the CRe′ signal, the DPCM will transmit the QC signal, and the APCM will transmit the QCA signal. In contrast to the above description where the APCM initiates the call, the APCM may transmit an additional signal or sequence to suitably identify the transition sequence signal points to the DPCM (rather than embedding the signal points in the CRe′ or QCA sequences).

[0060] Following task 410, the DPCM may perform a task 412 to obtain the signal points (or point) for use in a transition (or synchronization) sequence. As discussed above, the QC signal preferably conveys information that identifies signal points that make the presence of robbed bit signaling easily detectable by the APCM. The determination of the particular signal points may be carried out by the APCM, as described above in connection with the digital impairment learning procedure 364 (see FIG. 3). This determination may be based on past analyses of the digital impairments associated with a previous connection over the same channel. Task 412 may be performed by processor 312 after the APCM receives the QC signal.

[0061] In response to task 412, a task 414 may be performed such that a suitable transition sequence is transmitted by the DPCM. In an exemplary embodiment, the transition sequence includes positive and negative values of the signal points obtained in task 412. Accordingly, the DPCM may utilize the signal points selected by the APCM and a suitable sign pattern (which may be predetermined) to generate the transition sequence. The transition sequence is configured and formatted such that the APCM, upon detecting the transmission sequence, can synchronize itself to the subsequent signal or sequence transmitted by the DPCM. In this manner, the APCM receiver can obtain its timing from the transition sequence. The transmission sequence may be of any predetermined length and have any predetermined sign pattern. For example, in the embodiment depicted in FIG. 5, the transition sequence is represented by the quick timing sequence (QTS) and QTS\ signals, where QTS represents a specific signal point sequence and QTS\ is the same sequence having opposite signs. In FIG. 5, the QTS sequence is repeated for 810 symbols while the QTS\ sequence is repeated for 30 symbols.

[0062] In accordance with one practical embodiment of the present invention, the QTS sequence is formatted such that the period of the QTS root sequence and the period of the robbed bit signaling (“RBS”) associated with the network connection have no common denominator (other than one). For example, one suitable QTS root sequence is 0, +A, −A, +A, −A (where A represents a signal point that highlights the presence of RBS. Thus, for the embodiment illustrated in FIG. 5, this QTS root sequence, which has a period of five, is repeated 162 times while the QTS\ sequence includes six repetitions of the root QTS sequence with inverted signs.

[0063] For the above example, where the RBS period is assumed to be six, the received transition sequence may be subjected to a 30-point discrete Fourier transform (“DFT”) to obtain the timing phase of the DPCM. In addition, the presence of RBS will be revealed at certain discrete frequencies associated with the DFT result. In this manner, timing and RBS information can be extracted from the received transition sequence. In addition, the timing phase information is obtained independently from the RBS information.

[0064] The DPCM is preferably configured to transmit a specific signal point sequence during a task 416. The signal point sequence may be considered to be a modified answer tone, as that term is understood by those familiar with modem protocols. In FIG. 5, this signal point sequence is represented by the ANSpcm signal. As depicted in FIG. 3, a predetermined ANSpcm sequence 338 may be stored in memory element 320 for transmission by transmitter section 316. In a practical embodiment, the DPCM transmits the ANSpcm signal following the transition sequence. This may be desirable to enable the APCM to anticipate the signal point sequence once it detects the transition sequence. In other words, the detection of the transition sequence by the APCM will indicate that the signal point sequence will follow.

[0065] In a preferred embodiment, the ANSpcm signal comprises a sequence of pulse code modulation signal points or a sequence of signal points associated with pulse code modulation signal points. For example, the ANSpcm signal may be formatted as a sequence of mu-law or A-law codewords or a sequence of universal codewords (U-codes). The APCM and the DPCM are preferably configured such that the ANSpcm signal is predetermined and known prior to the initiation of quick startup process 400. In an alternate embodiment, a number of different ANSpcm signals may be suitably stored in lookup tables or the ANSpcm signal may be designed by one of the modem devices and communicated in a suitable manner to the other modem device prior to task 416. For example, the ANSpcm signal may be designed such that the presence of RBS can be easily detected by the APCM by analyzing the received ANSpcm signal. In such an embodiment, it may not be necessary for the transition sequence (QTS and QTS\) to identify or highlight the RBS.

[0066] In the context of V.8, the answer tone is generated as an amplitude modulated 2100 Hz tone. In contrast, the present invention utilizes the ANSpcm signal to generate a tone (e.g., a 2100 Hz tone) in a digital manner using pulse code modulation signal points. In other words, the ANSpcm signal is a digital representation of an analog signal. The ANSpcm signal is preferably constructed with known pulse code modulation points such that the ANSpcm signal may be used for purposes other than a mere answer tone. In a preferred embodiment, the ANSpcm signal includes many of the available pulse code modulation points associated with the particular telephone network. This aspect of the ANSpcm signal is desirable such that the ANSpcm signal may be used to determine or identify the characteristics of the current communication channel, particularly digital pads. The use of a large number of the possible codewords ensures that the ANSpcm signal will detect digital pads that may merge two input levels into one output level. The ANSpcm signal is also configured to provide a tone suitable for disabling the network echo cancelers and disabling the network echo suppressors.

[0067] If the ANSpcm signal is defined using look-up tables, a practical implementation may be difficult where multiple transmit levels are contemplated or required. For example, ITU-T Recommendation V.90 allows the DPCM to specify 32 different transmit levels. Storing a separate table for each transmit level may thus lead to excessive memory requirements. Accordingly, in an alternate embodiment, a procedure may be defined for mapping a plurality of codewords associated with one transmit level into a corresponding plurality of codewords associated with the other transmit levels. For example, given a table of PCM codewords defining the ANSpcm signal for a level of −0.5 dBm0, the procedure may involve mapping each individual PCM codeword to its corresponding PCM level, scaling that level according to the desired transmit level reduction, quantizing the resulting level back to the closest PCM level, and converting to the corresponding PCM codeword. Thus a corresponding ANSpcm signal can be constructed using the same mechanism in both the DPCM transmitter and the APCM receiver, hence producing the identical sequence of PCM codewords on each side. Note that, in accordance with this embodiment, the quantizing rule should be exact in dealing with “ties” in the quantization, i.e., if two PCM levels are equidistant from the scaled level. For example, the rule may dictate that, in case of a tie, the PCM level closer to zero is selected.

[0068] In accordance with yet another embodiment, the overall method of defining the ANSpcm signal could be based on a predetermined algorithm that generates the sequence of PCM codewords representing the ANSpcm signal. For example, the signal could be defined as a collection of tones, 2100 Hz being the strongest, where the tones have predefined amplitudes and initial phases. The sum of the tones would then be scaled according to the desired transmit level, and the resulting signal would be quantized to the closest PCM level, again using an exact quantizing rule in case of a tie. However, this method would also employ an exact definition of either the sine or cosine function, as well as how many bits were accumulated in summing the tones, to ensure that the calculations proceed in a consistent manner at both ends such that the ANSpcm signal can be properly detected.

[0069] As described above, the APCM anticipates the transmission of the ANSpcm signal. The digital impairments and analog characteristics associated with the communication channel will affect the ANSpcm signal as it is transmitted from the DPCM to the APCM. A task 418 may be performed by the APCM to obtain a received sequence that is related to the ANSpcm signal point sequence. The APCM may then perform a task 420 to compare a number of attributes of the received sequence with a number of stored attributes of a previously received sequence associated with a previously established communication channel. In an illustrative embodiment, the previously received sequence is a digital impairment learning (“DIL”) sequence, which is a line probing sequence. In this respect, task 420 determines whether a characteristic of the current channel is similar to a corresponding characteristic of a previously established channel. In a preferred embodiment, the channel characteristics compared in task 420 are related to the digital impairments in the channel. In other words, task 420 validates a current digital impairment channel profile with a stored digital impairment channel profile. Task 420 may be performed by a suitable processor element of the APCM (see FIG. 3.).

[0070] During task 420, any measurable characteristic of the points/levels, any measurable characteristic of the received sequence as a whole, and/or any measurable signal or quantity associated with the points/levels may be analyzed by the APCM. For example, any number of individual points or levels contained in the received sequence may be compared to corresponding points or levels stored at APCM (the stored points or levels may be associated with a prior DIL procedure). If the received points/levels “match” the stored points/levels or if the differences between the received and stored points/levels are within a certain threshold, then the APCM may assume that the current channel attributes match the stored channel attributes (see query task 210 in FIG. 2).

[0071] The APCM may perform a procedure 421 to suitably obtain and save a number of attributes or characteristics of a previously established connection to the current channel. As described above, procedure 421 may cause the APCM to store the characteristics of the points/levels contained in a received DIL sequence. These past values are thereafter used during task 420. In this respect, procedure 421 may update the previous values with new DIL values after the comparison in task 420 is completed, e.g., in response to a subsequent DIL procedure associated with the current connection.

[0072] As described above in connection with FIG. 2, if task 420 determines that the channel characteristics do not sufficiently match, then the modem system may revert to a conventional V.90 startup procedure. FIG. 5 illustrates that the APCM may fall back into the V.8 protocol and transmit a conventional V.8 call menu (CM) message to the DPCM. The conventional V.8 startup for the APCM then follows along a sequence 502. In response to the CM message, the DPCM generates a conventional V.8 joint menu (JM) message and proceeds in accordance with the conventional V.8 initialization (indicated by a sequence 504). For the sake of illustration, quick startup process 400 assumes that task 420 determines that the current communication channel is similar to a previously established communication channel.

[0073] If the APCM validates the current channel characteristics with a previous channel, then it may trigger a quick startup routine to further reduce the initialization time associated with the modem system. Alternatively, the DPCM may be configured to trigger the quick startup routine. Accordingly, a task 422 may be performed, during which the modem system is initially trained. (For the sake of clarity and brevity, portions of task 422 and portions of the subsequent tasks may be performed by both the APCM and the DPCM; quick startup process 400 depicts such combined functionality in the context of single process tasks). Task 422 may cause the APCM and the DPCM to be initialized in response to a number of stored parameters associated with the previously established communication channel. As mentioned above, the stored parameters may be related to the initialization or training of the equalizers, echo cancelers, transmit power levels, initial signal point constellations, or the like. Task 422 may operate in conjunction with procedure 421, which preferably functions to obtain and store the initialization parameters associated with the previous connection. In this respect, procedure 421 may be suitably designed to periodically save such parameters during the normal data mode of the previous connection, after a renegotiation process, or in response to any condition or event associated with the previous communication session. Procedure 421 may also be configured such that erroneous settings or initialization parameters are not inadvertently saved.

[0074] In the context of a typical V.90 connection, task 422 may be related to a two-point training phase. Using the previous parameters, the modem system may be able to skip or abbreviate the conventional V.90 Phase 2 probing and ranging procedure and to skip or abbreviate the conventional V.90 Phase 3 digital impairment learning and initial training procedures. As shown in FIG. 5, the APCM and the DPCM may each transmit training sequences (represented by the TRNI signals) during task 422. These training signals may be utilized to adaptively adjust the equalizer and echo canceler filter taps and to otherwise facilitate training of the modem system. Thus, one of the most time consuming procedures of a V.90 startup (the training of the APCM equalizer) can be performed in an efficient manner that allows ample time for fine tuning and training.

[0075] In addition to the initial training that occurs during task 422, a task 424 may be performed. During task 424, the modem system may conduct error correction and/or data compression protocols. In a conventional V.90 modem system, the V.42 Recommendation is followed for purposes of error correction and the V.42bis Recommendation is followed for purposes of data compression. For example, in a normal V.90 operating mode associated with a PPP connection, the V.42 and V.42bis procedures are performed after final training and before the CHAP/PAP authentication procedure. V.42 and V.42bis are performed prior to the CHAP/PAP procedure because the CHAP/PAP procedure is better suited to an “error free” channel. In contrast to conventional V.90 systems, task 424 may perform V.42bis during Phase 3 of the V.90 startup. The shifting of V.42bis forward in the startup process contributes to the reduction in connection time. In FIG. 5, the XID′ signal represents a modified version of the conventional V.42 XID signal. For example, the XID′ signal may utilize a subset of the XID parameters used to negotiate compression and the like. Portions of the V.42bis procedure may also be conducted in connection with various modified signal sequences shown in FIG. 5. For example, the CPt′ signal may represent the conventional V.90 CPt signal combined with one or more V.42bis signals.

[0076] In the preferred embodiment, the V.42bis procedures are performed to provide a substantially “error free” channel. Following task 424, a CONNECT message is issued to the host software. The CONNECT message indicates that the modem system is ready to transmit data at an initial data rate at this time. The CONNECT message may be formatted, generated, and transmitted in accordance with known techniques.

[0077] In response to the CONNECT message, the host software begins a “simultaneous” upper layer protocol login procedure, e.g., a CHAP or PAP procedure (task 428). Task 428 may be initiated automatically by the host software or in response to a user entry. The CHAP/PAP data transmission occurs in conjunction with a final training process. In the preferred embodiment, the APCM and the DPCM transmit the CHAP/PAP authentication data as scrambled digital data over the communication channel. The scrambling of the authentication data enables the modem devices to perform final training on the authentication data. In a conventional V.90 modem system, the final training signals are formatted as scrambled “ones”. The scrambled ones carry no information; the final training signal is merely utilized as a spectrally white source. The present invention leverages the final training signals to carry user data while the modem devices complete the training process. Although CHAP/PAP data is one preferred form of user data, the present invention is not limited to the transmission or exchange of authentication data. In addition, the particular scrambling algorithm may vary from application to application.

[0078] In FIG. 5, the dual function signals are represented by the TRN2A/PPP and TRN2D/PPP signals. In this respect, the receiver sections in the modem devices may be trained at an initial data rate during a first time period, e.g., during a data phase one, such that they may seamlessly transfer to operating at a final data rate during a subsequent time period, e.g., during a data phase two. Furthermore, the PPP log-in procedure can be performed at the initial data rate during the first time period rather than after the modem system has been fully initialized.

[0079] During the initial data rate period, a task 430 may be performed to enable the APCM and the DPCM to exchange constellation parameters and modulation parameters (represented by the CP and MP signals in FIG. 5) in a suitable manner. Task 430 may be performed in a conventional V.90 manner. These parameters may be utilized by the modem devices during the subsequent data mode. After the training and authentication procedures are completed, the modem system preferably transitions to a full data rate in a seamless manner. A task 432 may be performed to conduct data transmission at the full data rate. This period may be referred to as the data phase two. Once the modem system enters the full data mode, quick startup process 400 ends.

[0080] In contrast to the conventional V.90 modem startup summarized in Table 1, a modem system according to the present invention may experience a reduced startup latency, as set forth in Table 2 below. Notably, the startup time summarized in Table 2 is approximately half of the startup time summarized in Table 1. The considerable reduction in startup latency would be desirable in many situations, particularly in the context of a PPP dial-up internet connection using V.90 or legacy 56 kbps modem systems. TABLE 2 Quick V.90 Modem Startup PROTOCOL OPERATION TIME (seconds) — Dialing 1 — Call Establishment 1 V.8 bis (abbreviated) Capabilities 1 Exchange — Modified Answer 1 Tone V.90 Phase 3 + V.42/V.42 bis Initial APCM 2.5 Training; Error Correction; Data Compression V.90 Phase 4 + Login Final APCM 2-5 Training; Set Power Levels; Constellation Trans- mission; Username & Password TOTAL = 8.5-11.5

[0081] The techniques of the present invention may be implemented in other contexts to reduce the reinitialization time associated with reconnects after a line corrupting event or a channel interruption. For example, many telephone customers subscribe to call waiting, caller identification, and other telephony services. However, such services may be disabled or nonfunctional if the telephone line is being utilized for a modem connection. If call waiting is not disabled during a modem connection, then the signal tones may interrupt the modem connection. If the user decides to answer the waiting line, then the off-hook and on-hook flash may cause the modem system to retrain its receivers or prompt a full reconnect procedure.

[0082] Rather than perform a time consuming reconnect or retrain procedure, a modem system may be configured to utilize stored analog and digital impairment information, equalizer settings, power levels, echo canceler settings, constellations, and the like. Such stored information can be used to immediately reset the modem system parameters if the channel connection is interrupted by a call waiting procedure, by an off-hook condition at an extension telephone device, by a caller identification request, or by any channel corruption event, whether such event is planned or unintentional. In this scenario, both the client modem and the server modem may store the relevant system attributes, modem operating parameters, channel characteristics, and/or network characteristics.

[0083] In one practical example, in response to a call waiting tone, the client modem may signal the server to enter a standby mode. The server modem can then switch into an FSK mode to suitably detect the Class 2 caller identification information while the server idles. If the user wants to answer the second call, then the client modem may periodically transmit standby signals or heartbeat tones to the server to instruct the server to continue holding. When the second call ends and the user desires to commence the data call, the client modem would commence a quick reconnect handshaking protocol (described below). On the other hand, if the user wants to terminate the first call, then a clear down message may be sent (alternatively, the periodic hold signal may end).

[0084] The quick reconnect handshake causes the modem devices to recall the saved parameters and attributes of the “held” channel and the saved operating parameters associated with the modem devices, as described briefly above in connection with previous channel parameters 342 and 382. With this technique, the modem system can be reconnected in a matter of seconds. Thus, the data mode user will not suffer the long reconnect penalty after handling an incoming call waiting or caller identification signal. The data mode user, using call waiting in this fashion, would be capable of accepting intermittent interruptions without noticeable delays associated with the modem connection.

[0085] This feature may be utilized to simulate an “always connected” mode with conventional PPP modem connections. For example, pertinent channel compensation information may be periodically saved for a given connection between a client modem and a server modem. The client user may answer incoming second line calls while pausing the data mode as described above. In addition, the data mode may be gracefully terminated if the client user initiates an outgoing voice call. After the voice call terminates, the client modem may re-dial or otherwise re-contact the server modem and establish a quick connection using the stored parameters.

[0086]FIG. 7 is a flow diagram illustrating portions of a quick reconnect process 700 performed by two modem devices, and FIG. 6 is a timing diagram 600 corresponding to an illustrative quick reconnect process performed by two modem devices. Timing diagram 600 may include acronyms and abbreviations that are often used in the context of conventional data communication protocols. The use of such terminology herein is intended to illustrate the concepts of the present invention in the context of one practical embodiment. However, the present invention may be employed in any suitable context, and the specific signals, number of sequences, timing of the sequences, data rates, and interaction between the two modem devices shown in FIG. 6 are not intended to limit the scope of the invention in any way.

[0087] Quick reconnect process 700 may be performed by a modem system after such modem system has established a communication session and, typically, after the modem system has entered a full-rate data mode. For purposes of this description, it may be assumed that the modem system is configured as described above (or is configured in an appropriate manner to support the various process tasks described below). It may be assumed that the two modem devices that perform process 700 are compatible with the quick reconnect techniques described herein. Thus, process 700 need not perform any verification or signaling to determine whether the quick reconnect procedure can be carried out.

[0088] Although not a requirement of quick reconnect process 700, the modem system may have been initialized in accordance with the quick startup techniques set forth above. Accordingly, process 700 assumes that both modem devices have stored any number of appropriate channel characteristics, receiver parameters, and other information relevant to the initialization, training, and synchronization of the modem system. As described above, such information may be suitably saved during a startup procedure or periodically during a suitable data mode. Process 700 may be utilized to enable the current modem connection to be quickly re-established following a temporary pause in the modem data mode or any interrupting event. In this context, a practical system can maintain a communication link or connection between the modem devices while allowing a user of the client modem device to temporarily pause the modem connection (or the modem data communication mode). During the temporary holding period, the user may be able to answer another incoming call in response to a call waiting signal, initiate a new outgoing call, or the like, while the client side modem device idles.

[0089] Quick reconnect process 700 may begin with a task 702, during which a reconnect indication is received by the DPCM (e.g., modem 302 shown in FIG. 3). The reconnect indication may be generated in response to a request (e.g., a user-initiated request) to terminate a temporary pause in the modem communication session. For example, a suitable reconnect signal may be generated by the APCM (e.g., modem 304) in response to a hook flash initiated by the user of the APCM or in response to an instruction generated by application software associated with the APCM. Alternatively, the APCM or a data access arrangement (DAA) associated with the APCM may generate a reconnect signal in response to a change in line current related to the on-hook status of telephone set. Such line-in-use detection techniques are generally known to those skilled in the art. The reconnect indication informs the DPCM that the user desires to re-establish the current modem connection, which has been placed on temporary hold. In a practical embodiment, the DPCM receives the reconnect indication and initiates a task 704 in response to the reconnect indication.

[0090] During task 704, the DPCM transmits a suitable reply signal that preferably informs the APCM that the quick reconnect procedure is supported. In the illustrative embodiment described herein, such a reply signal may include a suitable transition sequence as described above. Accordingly, quick reconnect process may perform a task 704, which may be similar to task 414 described above in connection with FIG. 4. For example, task 704 may cause the DPCM to transmit the QTS signal to enable the APCM to again determine the timing phase of the DPCM (the QTS signal is identified by reference number 602 in FIG. 6). In addition, the retransmission of the QTS signal enables the APCM to obtain RBS characteristics of the data communication network (if necessary or desirable to do so).

[0091] It should be noted that, for many practical modem connections, the network connection (and the associated effects of digital pads and RBS) will remain consistent during the modem hold period. Of course, there may be some situations where the network connection is cleared down during the modem hold period to conserve network resources. In such situations, particularly if the same network connection is not re-established, the digital impairment profile of the network may not remain consistent. Furthermore, even if the network characteristics do not change, the APCM may lose its RBS synchronization if the modem connection is put on hold (particularly if the APCM does not receive a signal from the DPCM during the holding period). In this respect, even if the APCM can properly resynchronize itself to the network clock after a holding period, the specific RBS phases may still be unknown. Accordingly, quick reconnect process 700 is preferably arranged to contemplate that the network connection and the RBS timing has changed.

[0092] The reply signal may also include a suitable signal point sequence that follows the transition sequence. Accordingly, following task 704, the DPCM may perform a task 706 to suitably transmit a signal point sequence to the APCM. As described above in connection with task 416, the signal point sequence may be considered to be a modified answer tone, e.g., the ANSpcm signal (identified by reference number 604 in FIG. 6). The ANSpcm signal 604 may be configured as described above, e.g., the ANSpcm signal 604 may be suitably formatted to enable the APCM to determine or identify the characteristics of the current communication channel or network, particularly digital pads and/or other digital impairments. The ANSpcm signal 604 is also configured to provide a tone suitable for disabling the network echo cancelers and disabling the network echo suppressors.

[0093] In a practical embodiment, the APCM anticipates the transmission of the ANSpcm signal 604. For example, the APCM may be configured to condition its receiver to receive the ANSpcm signal 604 after it transmits the reconnect indication to the DPCM. Accordingly, quick reconnect process 700 may include a query task 708, which preferably determines whether the ANSpcm signal 604 has been received by the APCM and/or whether the DPCM receives a suitable acknowledgment that the APCM received the ANSpcm signal 604. If not, then process 700 may exit and the modem system may proceed with a traditional reconnection routine. If query task 708 determines that the ANSpcm signal 706 was properly received, then the APCM may process the received signal as described above to enable the APCM to determine the digital impairments associated with the re-established channel.

[0094] A task 710 is preferably performed to cause both modem devices to recall and obtain the characteristics and parameters associated with the previous channel connection, i.e., the channel before the modem connection was placed on temporary hold. Task 710 may cause the DPCM to access previous channel information 342 and may cause the APCM to access previous channel information 384. As described above, this information may include one or more parameters related to: the current channel conditions (as previously determined), any number of settings associated with the modem receivers, characteristics of the communication network, or the like. Task 710 enables the modem system to quickly retrieve these stored parameters and reset the modem devices in an appropriate manner in lieu of an independent reassessment of the channel and in lieu of a full retraining process. Task 710 may be performed by the DPCM once it receives the reconnect identifier from the APCM, while task 710 may be performed by the APCM before it receives the ANSpcm signal 604. If task 710 is performed by the APCM, the APCM equalizers are initialized according to the previous channel information 384 such that the ANSpcm signal 604 can be properly received and analyzed.

[0095] The DPCM may reacquire its timing synchronization in accordance with any number of techniques, such as the conventional V.34 half-duplex primary channel resynchronization procedure set forth in ITU-T Recommendation V.34 (International Telecommunication Union, September 1994), which is incorporated by reference herein. In other words, as shown in FIG. 6, the APCM may be configured to transmit a PP signal 610 to enable the DPCM receiver to synchronize its timing recovery and carrier recovery. The S and S\ preamble signals (reference numbers 606 and 608, respectively) may be used to initialize an automatic gain control element or the like. The B1 signal 612 may be considered to be a preamble sequence that may be employed to initialize the DPCM scrambler, trellis coder, and the like. These signals and sequences are set forth in detail in the V.34 Recommendation and will not be described in detail herein.

[0096] Concurrently, the DPCM may transmit an R signal 616 followed by an R\ signal 618 and a B1 signal 620. These sequences also serve as suitable preamble sequences that enable the APCM to prepare for the data mode. These signals and sequences are set forth in detail in the V.90 Recommendation and will not be described in detail herein.

[0097] In response to the resynchronization sequences, the modem system enters the data mode and the system can begin transmitting data at the full data rate (task 712). In other words, the data transmission mode is re-established without completely clearing down the previous connection. The data mode is identified by sequences 614 and 620 in FIG. 6. Notably, in contrast to quick startup process 400, quick reconnect process 700 need not perform a comparison of the channel characteristics (see task 420), an initial training procedure (see task 422), an error correction and data compression procedure (see task 424), a final training procedure (see task 428), an authentication exchange (see task 428), or an exchange of constellation and modem parameters (see task 430). With respect to the PAP/CHAP authentication information, the modem system may be suitably configured to maintain the PPP/TCP/IP protocol layer during the hold period such that the PPP authentication data need not be retransmitted. Accordingly, the modem system may re-establish its modem connection without wasting time performing several traditional initialization tasks. In a typical practical system, the quick reconnect process can be employed to reestablish the data mode in less than 1.5 seconds.

[0098] An alternate version of the quick reconnect procedure may employ a timing diagram similar to timing diagram 500 (see FIG. 5). However, in such an embodiment, several of the signal segments described above in connection with timing diagram 500 can be reduced in length, thus reducing the conventional reconnect time. For example, the various TRN training sequences and the parameter exchange signals may be shortened considerably because they need not convey essential information. For practical implementation reasons, it may be desirable to keep the general sequence structure intact in this manner (instead of eliminating segments from timing diagram 500). Indeed, from a software implementation standpoint, segment lengths can be adjusted in a relatively straightforward manner, while the removal of entire segments from an existing protocol may be a time consuming and arduous task. Although the reconnect time for such an alternate embodiment may be longer than that described above in connection with timing diagram 600 (e.g., up to 2.5 seconds), it is still significantly less than the time required to perform a conventional reinitialization procedure.

[0099] As mentioned previously, call waiting and related telephony features can be troublesome when the line is being used for a modem connection. In response to a call waiting alert signal, the modem connection is often disrupted without the modem devices being aware of the cause of the disruption. The call waiting alert signal may cause the modem devices to disconnect or to enter a lengthy retraining mode. Furthermore, in many scenarios the consumer is unable to take advantage of the call waiting service itself. Generally, the present invention addresses this problem in the following ways: (1) by allowing either modem device to request an immediate clear down in response to a call waiting alert; (2) by allowing a first modem device to request the second modem device to go on-hold, and allowing the second modem device to grant or deny the request; and (3) by allowing either modem device to request a quick reconnect procedure (as described above). With this signaling technique in place, the modem connection can either be cleared down, put on hold, or quickly reconnected in response to an alert signal, e.g., a call waiting alert. Similarly, if the modem connection is put on-hold, then the same signaling mechanism can be employed to reconnect the modem session after the holding period.

[0100] Assuming that both end devices (e.g., the DPCM and the APCM in a V.90 system) are compatible with the modem-on-hold feature, an appropriate signaling scheme is utilized to enable the end devices to switch operating modes as necessary. Although the signaling scheme and various processes are described herein in the context of a modem system having an APCM at the client end and a DPCM at the server or central site end, the present invention is not so limited. For example, the techniques described herein may be equivalently applied in the context of a communication session between two client modem devices or in the context of a V.34 modem system.

[0101]FIG. 16 is a schematic representation of an exemplary environment in which a modem system 1600 may operate. Modem system 1600 generally includes a first modem device 1602, which may be associated with a central site, and a second modem device 1604, which may be resident at a customer site 1670. In the context of a typical V.90 system, first modem device 1602 may be the DPCM and second modem device 1604 may be the APCM. DPCM 1602 is coupled to a central office 1606 via a digital link and APCM 1604 is coupled to central office 1606 via an analog link, e.g., the local loop. It should be appreciated that modem system 1600 may include additional elements and functionality associated with the quick startup routine and/or the quick reconnect procedure described above.

[0102]FIG. 16 also depicts a calling device 1608 (which is capable of placing an incoming call to the customer site), a parallel answer device 1610 located at the customer site, and a series answer device 1611 located at the customer site. As shown in FIG. 16, parallel answer device 1610 is connected such that it receives the same calls as APCM 1604 in a concurrent manner. In contrast, series answer device 1611 is connected such that APCM 1604 routes calls to it; APCM 1604 may control or regulate the call traffic to and from series answer device 1611 in a conventional manner. A call may be established between calling device 1608 and answer devices 1610 and 1611 via central office 1606, and a modem connection may be established between DPCM 1602 and APCM 1604 via central office 1606.

[0103] Generally, the modem system is configured to support a signaling mechanism that responds to call waiting and other situations that may call for an interruption in the modem connection. For example, APCM 1604 may transmit a suitably formatted signal to initiate a modem-on-hold state, DPCM 1602 may transmit a different signal to acknowledge the modem-on-hold request, APCM 1604 may transmit yet another signal to request that a quick reconnect procedure (as described above) be initiated, and either modem device may transmit a signal that represents a clear down request. For the sake of clarity and brevity, FIG. 16 depicts APCM 1604 and DPCM 1602 in a manner that relates to the example processes described herein. In practical embodiments, each of the modem devices may be capable of functioning as a transmit or receive modem, and each of the modem devices may be capable of originating the various signals described herein.

[0104] DPCM 1602 includes a transmitter section 1612 and a receiver section 1614, both of which may be configured in accordance with conventional technologies and in accordance with the above description of modem system 300 (see FIG. 3). DPCM 1602 is capable of transmitting a number of signals, sequences, and tones during initialization procedures, the data mode, the hold mode, and transition modes. As described above, DPCM 1602 may be configured to transmit a suitable transition sequence 1616 and a characteristic signal point sequence (such as the ANSpcm signal 1618) associated with a quick startup routine or a quick reconnect procedure. During the data mode, DPCM 1602 transmits data 1620 in accordance with a suitable data transmission scheme.

[0105] DPCM 1602 is also capable of transmitting a number of signals that may be received by APCM 1604 and/or by central office 1606. For example, DPCM 1602 is capable of transmitting an “A” tone 1622 and a “B” tone 1624 as described herein. In one practical embodiment, “A” tone 1622 is a 2400 Hz tone and “B” tone 1624 is a 1200 Hz tone (as set forth in ITU-T Recommendation V.34). Of course, the modem devices may generate and process any suitable tones or signals in lieu of (or in addition to) these predefined tones. DPCM 1602 is also configured to transmit a number of additional signals associated with the initiating of a modem-on-hold mode, the reconnection of a modem session after a holding period, and the clearing down of a modem connection. For example, DPCM 1602 may be capable of transmitting a modem hold request 1626, a modem hold acknowledgment 1628, a quick reconnect request 1630, and a disconnect signal 1632 (referred to herein as “modem status signals”). The format and function of these signals are described in more detail below. DPCM 1602 may also include a signal detection element 1634, which may employ any number of known techniques to detect, analyze, and interpret control signals, requests, and tones transmitted by APCM 1604 and/or by central office 1606. For example, signal detection element 1634 may utilize a conventional tone detector and/or a conventional V.34 or V.90 differential phase-shift keying (DPSK) receiver configured to detect and distinguish the different signals described herein.

[0106] For purposes of the signaling scheme described herein, APCM 1604 is preferably configured in a manner similar to DPCM 1602. In other words, APCM 1604 is capable of transmitting an “A” tone 1642, a “B” tone 1644, a modem hold request 1646, a modem hold acknowledgment 1648, a quick reconnect request. 1650, and a disconnect signal 1652. In addition, APCM 1604 may be configured to generate a caller ID tone 1654 that informs central office 1606 that the customer site supports a caller ID feature (as depicted by the caller ID component 1656). In accordance with current standards, caller ID tone 1654 is a DTMF “D” tone having a length of approximately 55-65 milliseconds. Of course, APCM 1604 transmits data 1658 during the data mode.

[0107] As described above in connection with DPCM 1602, APCM 1604 preferably includes a signaling detection element 1660 that enables APCM 1604 to receive, detect, and analyze the various signaling tones and sequences transmitted by DPCM 1602. In this manner, both APCM 1604 and DPCM 1602 are capable of receiving the signals and are capable of switching operating modes in response to the particular signal or signals that are received.

[0108] Central office 1606 is configured in a conventional manner to perform circuit switching associated with modem, voice, and facsimile calls. Central office 1606 may support any number of customer sites and central office 1606 may be operatively coupled to any number of other central offices, central site modems, or the like. As described briefly above, APCM 1604, answer device 1610, and caller ID component 1656 may reside at customer site 1670. Accordingly, APCM 1604, answer device 1610, and caller ID component 1656 are all supported by central office 1606.

[0109] Central office 1606 includes a suitable switching fabric 1672 for routing calls between the appropriate parties. For example, switching fabric 1672 may switch to a first state to establish a modem connection between DPCM 1602 and APCM 1604 and to a second state to establish a voice connection between calling device 1608 and answer device 1610. Furthermore, switch fabric 1672 may be capable of temporarily interrupting a connection to impress control signals, data, or tones onto the current circuit or line. In this respect, central office 1606 may transmit a number of ring signals 1674, alert signals 1676, caller ID data 1678, and other information depending upon the particular situation. For example, in accordance with current methodologies, central office 1606 may temporarily interrupt a voice call and transmit a call waiting alert signal 1676 to the customer site 1670. If the customer accepts the incoming call, then switch fabric 1672 may be reconfigured to route the incoming call the customer site 1670 while the original call is placed on hold. As described in more detail below, a similar routine may be employed to place modem calls on hold.

[0110] As mentioned previously, the signaling scheme preferably employs Phase 2 signaling tones that are also used by conventional V.34 and V.90 modem systems. In addition, the signaling scheme uses DPSK transmission techniques, which allows the signaling to integrate in a seamless manner with V.34 and V.90 retraining procedures. The signals are configured such that they can be detected by either a V.34/NV.90 DPSK receiver or by a relatively simple tone detector. In one practical embodiment, modem hold requests, modem hold acknowledgments, quick reconnect requests, and disconnect signals are preceded by a period (e.g., at least 50 milliseconds) of either tone A or tone B. This technique leverages the use of the A and B tones, which are employed by conventional V.34 and V.90 modem systems, and takes advantage of the modulation scheme that is already in use by the modem system. Thus, because DPCM 1602 will typically be conditioned to receive DPSK signals, the signaling mechanism is easy to implement.

[0111] The modem status signals that follow the A or B tones are preferably transmitted as DPSK signals based on a repeated bit pattern. In the preferred embodiment, a modem status signal is a DPSK signal associated with eight repetitions of a four-bit pattern, where different patterns correspond to different modem status signals. The use of a four-bit pattern is desirable to enable the use of a simple tone detector for signaling detection elements 1634 and 1660; shorter bit patterns result in a fewer number of frequency components associated with the DPSK signal. Consequently, the signal detection scheme need not employ a complex processing routine that analyzes a large number of frequencies for spectral content. Illustrative bit patterns for the different modem status signals are set forth in Table 3 below. TABLE 3 Modem Status Signals Modem Status Signal Signal Abbreviation DPSK Pattern Disconnect Signal DC 0101 Modem Hold Request MH 0011 Modem Hold Acknowledge MHA 0001 Quick Reconnect Request QRR 0111

[0112] The particular bit patterns are preferably selected such that the resultant DPSK signal is distinguishable over DPSK signals that are “reserved” for use in the context of other data communication protocols. For example, a DPSK pattern of all zeros is equivalent to the A or B tones, and a DPSK pattern of all ones is equivalent to the V.34 INFOMARK signal. In addition, the particular bit patterns may be suitably selected such that the resultant DPSK signal is easy to detect by a tone detector. For the example bit patterns set forth in Table 3, the modem status signals will have the frequency content listed in Tables 4 and 5 below, where the frequencies are in Hertz, an “X” indicates spectral content greater than a threshold level, and a slash indicates spectral content that is lower than the threshold level. For the example DPSK bit patterns shown in Table 3, a lower spectral energy component is at least 8 dB down from a higher spectral energy component at the same frequency. Consequently, the different modem status signals can be distinguished notwithstanding the existence of some shared frequency components. TABLE 4 Frequency Components for Modem Status Signals (APCM) 900 975 1050 1125 1200 1275 1350 1425 1500 DC X X MH X X X X X MHA — X X — QRR X — — X

[0113] TABLE 5 Frequency Components for Modem Status Signals (DPCM) 2100 2175 2250 2325 2400 2475 2550 2625 2700 DC X X MH X X X X X MHA — X X — QRR X — — X

[0114] The different frequency ranges employed by the APCM and DPCM are related to an exemplary application where different carriers are used by the two modem devices. For example, in a conventional V.90 system, the DPCM uses signaling near 2400 Hz (tone “B” and the DPSK carrier), while the APCM uses signaling near 1200 Hz. This feature was derived from the conventional V.34 scheme where the calling modem uses signaling near 1200 Hz and the answer modem uses signaling near 2400 Hz. Consequently, the two spectral patterns are the same but for the shift between 1200 Hz and 2400 Hz. This methodology ensures that the end devices can properly detect the signals even where both ends are transmitting the same type of signal.

[0115] In a practical system, the modem status signal detection need not detect the entire “spectral fingerprint” for the given signals. Rather, signal detection elements 1634 and 1660 may be configured to detect and analyze a distinctive number of the spectral components for purposes of indicating a match. For example, as shown in Table 4, if a signal contains relatively high spectral energy at 1050 Hz and 1350 Hz, then the signal may be a disconnect signal or a modem hold request. Accordingly, the signal detection routine will continue to analyze the signal for spectral content at 900 Hz, 1200 Hz, and/or 1500 Hz and make the appropriate decision.

[0116]FIG. 8 is a timing diagram that depicts the situation where a current modem connection is interrupted by a call waiting indication and the modem connection is placed on hold while the incoming call is answered by the client end. FIG. 8 is applicable regardless of whether customer site 1670 employs parallel answer device 1610 or series answer device 1611. The progression of signals, sequences, tones, commands, and the like are shown with respect to an APCM, a DPCM, and a central office (the central office may be associated with signals to the APCM and signals to the DPCM). For convenience, the process associated with FIG. 8 is described herein in the context of modem system 1600.

[0117] During the data mode, central office 1606 temporarily interrupts the modem connection and sends an alert signal 802 to APCM 1604. The alert signal may be a conventional call waiting alert and it may include a component that is audible to humans (e.g., an audio tone) and a component that is detectable by data communication devices or machines. In accordance with most call waiting protocols, the alert signal components are transmitted in series. In response to alert signal 802, APCM 1604 may send a DTMF tone 804 to request caller ID information from central office 1606. As described above, tone 804 may be a short burst of a DTMF “D” tone having a duration of about 55-65 milliseconds. Assuming that central office 1606 receives and recognizes DTMF tone 804, it will format and transmit the caller ID data 805 back to the customer site 1670. As shown in FIG. 16, the caller ID data 805 (represented by reference number 1678 in FIG. 16) may be received and processed in a suitable manner for display or analysis by caller ID component 1656.

[0118] In response to the switching out of APCM 1604 by central office 1606, DPCM 1602 begins a retrain procedure by transmitting an appropriate signal, e.g., a “B” tone 806. In a practical application, the “B” tone 806 is usually transmitted while the caller ID request 804 and caller ID data 805 is being received, processed, and transmitted by central office 1606. The “B” tone 806 is continuously transmitted while DPCM 1602 waits for APCM 1604 to reply with an “A” tone 808. APCM 1604 may transmit the “A” tone 808 if it receives the “B” tone 806 from DPCM 1604. As mentioned above, the “A” tone 808 is preferably transmitted for at least a minimum duration, e.g., 50 milliseconds, to give DPCM 1602 the opportunity to receive it. If DPCM 1602 does not receive an “A” tone 808 within a specific time period, then it may eventually disconnect itself.

[0119] Assuming that the user of APCM 1604 desires to answer the incoming call, then a modem hold request 810 is transmitted following the “A” tone 808. Modem hold request 810 may be prompted automatically by a suitable device resident at the customer site 1670 or it may be prompted in response to a user command. Modem hold request 810, which may be formatted as described above, is preferably transmitted for at least a minimum period of time. In one practical embodiment, modem hold request 810 is transmitted for approximately 53 milliseconds (all of the modem status signals described herein may have a similar minimum duration). In contrast to a conventional V.34 or V.90 modem system, an actual retraining procedure is not performed upon receipt of the “A” tone 808 by DPCM 1602. Rather, in response to modem hold request 810, DPCM 1602 may transmit a modem hold acknowledgment 812 for a minimum period of time, e.g., approximately 53 milliseconds.

[0120] After DPCM 1602 transmits modem hold acknowledgment 812, it preferably continues to transmit the “B” tone 806 while it maintains a hold state. In response to modem hold acknowledgment 812, APCM 1604 may generate a suitable flash signal 814 to instruct central office 1606 to switch out the modem connection and to switch in the incoming call 816. In addition, the handset (or other suitable answer device) begins to receive the incoming call; APCM 1604 may be configured to route the incoming signal to parallel answer device 1610 or serial answer device 1611 in an appropriate manner. In addition, APCM 1604 may be placed in an idle or “on-hook” state while the handset is connected (during period 818). Accordingly, the user at customer site 1670 may proceed with the incoming call 816 while DPCM 1602 remains on hold. The modem connection may be re-established by way of a quick modem reconnect procedure (described below).

[0121]FIG. 9 is a timing diagram that depicts a situation where DPCM 1602 is to be reconnected in response to the termination of the incoming call. The process shown in FIG. 9 assumes that: (1) DPCM 1602 is in a hold state; (2) answer device 1610 is connected in parallel with APCM 1604; and (3) answer device 1610 terminates the incoming call, e.g., answer device 1610 is placed “on-hook” before calling device 1608 is placed “on-hook”. For purposes of this description, the parallel connection means that APCM 1604 and answer device 1610 receive the same signals from central office 1606 in a concurrent manner.

[0122] In response to the termination of the incoming call, central office 1606 will detect the “hang up” in a conventional manner, e.g., using well known line detection techniques. Eventually, central office 1606 switches out or disconnects the incoming call, switches in DPCM 1602, and generates a suitable signal, e.g., a ring signal 902. Ring signal 902 serves to alert the user at customer site 1670 that the original call is still holding and is ready to be reconnected. In response to ring signal 902, APCM 1604 is placed “off-hook” such that it can again receive signals from central office 1606. Thus, ring signal 902 may inform APCM 1604 that the incoming call has been cleared and/or that APCM 1604 may proceed with a modem reconnect procedure. As described above in connection with FIG. 8, APCM 1604 generates an “A” tone 904 (for at least 50 milliseconds) in response to the detection of a “B” tone 906. Following the “A” tone 904, APCM 1604 may transmit a quick reconnect request 908 to initiate a quick reconnect procedure (as described above in the context of FIGS. 6 and 7. Accordingly, in response to the detection of quick reconnect request 908, DPCM 1602 preferably transmits a QTS signal 910 followed by an ANSpcm sequence 912. The characteristics, format, and function of QTS signal 910 and ANSpcm sequence 912 are as described above. Assuming that both modem devices support the quick reconnect feature described above, the held modem connection may be re-established in a relatively short period of time.

[0123]FIG. 10 is a timing diagram that depicts the situation where the incoming call is terminated before parallel answer device 1610 is placed “on-hook”. In this scenario, when the termination of the incoming call is initiated by the calling device 1608, central office 1606 will reconnect the customer site 1670 to the original call (which is a modem connection in this example). Consequently, the “B” tone transmitted by DPCM 1602 will again be made available at APCM 1604. Regardless of whether APCM 1604 is currently in an “on-hook” or an “off-hook” state, it preferably detects that DPCM 1602 has been reconnected. It should be appreciated that APCM 1604 may employ any number of known techniques (which can vary depending upon the specific implementation) to detect the reconnection. For example, DPCM 1602 may detect the “B” tone from DPCM 1602, it may automatically react after a predetermined timeout period, or it may utilize line-in-use techniques to sense the termination of the incoming call. Once the two modem devices have resumed communicating with one another, the quick reconnect routine proceeds as described above in connection with FIG. 9.

[0124] With respect to the situation depicted in FIG. 10, it may be necessary to have APCM 1604 respond within certain time periods to ensure that central office 1606 does not consider the reconnect attempt to be a hook flash or a disconnect. For example, in a preferred embodiment, APCM 1604 is configured to respond to the termination of the incoming call within 200 milliseconds such that central office 1606 does not interpret the delay as a conference call request (which may cause DPCM 1602 to be placed on hold) or a disconnection (which may cause a clear down of the connection). The particular time periods may be selected in accordance with any suitable telecommunication recommendation, standard, or operating protocol, such as the BELLCORE Technical Reference GR-506-CORE (related to general telecommunication signaling) and the BELLCORE Technical Reference TR-NWT-000575. The contents of these references is incorporated by reference herein. In general, any of the procedures utilized in the context of a system using parallel answer device 1610 may also be used in the context of a system using series answer device 1611. However, the converse may not always be true. For example, FIG. 11 is a timing diagram that depicts the situation where the incoming call is terminated by series answer device 1611. As described above, a communication line at customer site 1670 initially provides APCM 1604 with a signal from central office 1606, and APCM 1604 routes the signal to answer device 1610. In most practical applications, APCM 1604 will remain “off-hook” even if it is merely routing the call to series answer device 1611. Accordingly, APCM 1604 is capable of monitoring the line for the presence of a “B” tone or a suitable signal associated with DPCM 1602. In this scenario, if the incoming call is terminated (by calling device 1608 or by series answer device 1611), APCM 1604 is capable of receiving signals from central office 1606. Furthermore, central office 1606 responds to the detection of the call termination by switching DPCM 1602 to communicate with the customer site 1670. Thus, if the “B” tone is detected by APCM 1604, it can immediately decouple the series answer device 1611. Once the two modem devices resume the communication session, the quick reconnect routine proceeds as described above in connection with FIG. 9.

[0125]FIG. 12 is a timing diagram that depicts the situation where DPCM 1602 responds to a modem hold request with a clear down instruction (FIG. 12 is applicable to a system that uses either serial answer device 1611 or parallel answer device 1610). Up to the point where a modem hold request 1202 is transmitted from APCM 1604 to DPCM 1602, the process is similar to that described above in connection with FIG. 8. In contrast to the scenario where DPCM 1602 acknowledges modem hold request 1202, the situation depicted in FIG. 12 calls for the transmission of a disconnect signal 1204 from DPCM 1602. DPCM 1602 may transmit disconnect signal 1204 after contemplating or considering any number of operating parameters, e.g., the current call traffic, the functional capabilities of DPCM 1602, the channel characteristics, or the like.

[0126] After DPCM 1602 transmits disconnect signal 1204, it idles or waits without transmitting any meaningful signals. In response to disconnect signal 1204, APCM 1604 clears down the modem connection in an appropriate manner. If central office 1606 does not detect activity from APCM 1604 after a suitable timeout period, e.g., 1550 milliseconds, then it may assume that APCM 1604 has been disconnected. Thereafter, central office 1606 switches out DPCM 1602 and generates ring signals 1206 and caller ID data 1208 to customer site 1670 such that the incoming call can be answered. DPCM 1602 may clear down its modem connection after a suitable timeout period, e.g., two seconds, during which it receives no signals from APCM 1604. Accordingly, DPCM 1604 will typically hang up once central office 1606 begins generating ring signal 1206. As described above, prior to clear down, APCM 1604 and/or DPCM 1602 may save any number of relevant operational parameters to facilitate a quick startup for subsequent connections.

[0127] Under certain conditions, the end user may wish to immediately terminate the modem connection and accept an incoming call. FIG. 13 is a timing diagram that depicts a situation where, in response to an alert signal 1302, APCM 1604 transmits a disconnect signal 1304 rather than a modem hold request. FIG. 13 is applicable to a system that uses either serial answer device 1611 or parallel answer device 1610. APCM 1604 may generate disconnect signal 1304 in response to a user command or automatically in accordance with a predetermined protocol or setting. The progression of signals and operations associated with FIG. 13 is substantially similar to the progression associated with FIG. 12. However, unlike the process depicted in FIG. 12, APCM 1604 transmits disconnect signal 1304 to DPCM 1602.

[0128]FIG. 14 is a timing diagram that depicts the scenario where, in response to an alert signal 1401, APCM 1604 prompts a quick reconnect procedure and ignores the incoming call. FIG. 14 is applicable to a system that uses either serial answer device 1611 or parallel answer device 1610. Such a situation may occur when the quality of the modem connection is important, when the end user does not want to be disturbed by incoming calls, and/or if the modem connection is severely affected by the alert signal 1401. Furthermore, such a situation may occur in response to the caller ID data, i.e., the answering party may choose to ignore incoming calls from certain calling parties. Up to the point where an “A” tone 1402 is transmitted, the procedure of FIG. 14 is similar to the procedure of FIG. 8. Following the transmission of “A” tone 1402, APCM 1604 generates a quick reconnect request 1404, which is eventually received by DPCM 1602. In response to quick reconnect request 1404, DPCM 1602 may transmit a QTS signal 1406 followed by an ANSpcm signal 1408 to facilitate the quick reconnect routine (as described above in connection with FIGS. 6 and 7). It should be noted that APCM 1604 may alternatively transmit a suitable modem status signal, e.g., a phase reversal, that indicates a full retrain procedure rather than a quick reconnect procedure. In such an embodiment, the retrain procedure would proceed in a conventional manner.

[0129] Under some conditions, DPCM 1602 may not “automatically” enter the initial retrain mode in response to an alert signal. In other words, DPCM 1602 may continue transmitting data as though no interruption has occurred. FIG. 15 is a timing diagram that illustrates this situation (FIG. 15 is applicable to a system that uses either serial answer device 1611 or parallel answer device 1610). As described above in connection with FIG. 8, APCM 1604 may respond to an alert signal 1502 by transmitting a DTMF “D” tone 1504 (associated with a caller ID request) during an interruption in the data mode. Unlike the situation of FIG. 8, where DPCM 1602 begins to transmit a “B” tone as a result of the interruption, DPCM 1602 continues to transmit data 1506 to APCM 1604. When APCM 1604 is reconnected by central office 1606, it preferably transmits an “A” tone 1508 for a suitable time period to allow DPCM 1602 to respond with a “B” tone 1510. When APCM 1604 detects the “B” tone 1510 from DPCM 1602, it then follows the “A” tone 1508 with a SIGNAL_(A) 1512, where SIGNAL_(A) 1512 may be a modem hold request, a quick reconnect request, or a disconnect signal. In response to SIGNAL_(A) 1512, DPCM 1602 transmits a SIGNAL_(D) 1514, where SIGNAL_(D) may be a modem hold acknowledgment, a short period of silence followed by a QTS signal and an ANSpcm sequence, or a disconnect signal. In this manner, the different situations described above can be handled even though DPCM 1602 does not initially enter the retrain mode with the transmission of a “B” tone.

[0130] The signaling routines and procedures described above in connection with FIGS. 8-16 can be equivalently applied to accommodate various requests that originate at customer site 1670. For example, the user of APCM 1604 may desire to place a current modem connection on hold, to prompt a quick reconnect, or to prompt a full retrain in an independent manner. In one practical embodiment, the modem hold request and modem hold acknowledgment signals can be incorporated into the conventional Phase 4 CP and MP sequences. Accordingly, if either modem device wants to place the other modem device on hold (e.g., for three-way calling), then the requesting modem device can perform a rate renegotiation and transmit the hold signal in an appropriate manner. This technique may be performed in a similar manner as the conventional V.34 and V.90 clear down procedure, where a special code (data rate=0) is used to indicate a clear down. However, the modem hold signaling technique may utilize a different bit combination or leverage a number of reserved bits.

[0131] In response to such a user request, APCM 1604 may generate an “A” tone followed by an appropriate modem status signal (e.g., a modem hold request, a quick reconnect request, or the like) for receipt by DPCM 1602. As described above in connection with FIG. 15, DPCM 1602 may then respond with a “B” tone followed by an appropriate status signal reply (e.g., a modem hold acknowledgment, a QTS signal, or the like). In this manner, the techniques of the present invention can be applied in any number of situations unrelated to a call waiting alert, a line interruption, or a line corrupting event.

[0132] In summary, the present invention provides techniques to reduce the initialization period and reconnect period normally associated with a V.90 modem system. The quick startup and quick reconnect techniques leverage the known channel characteristics of a previous connection to reduce the training time associated with subsequent attempts to establish the same connection. Although not limited to any specific modem application, the quick startup procedure may be used to eliminate portions of the initialization protocols or processes normally employed by a 56 kbps modem, e.g., V.8bis, V.8, digital impairment learning, initial training, probing and ranging, or the like. In addition, the quick startup technique may perform certain operations at a different time or in a different order in comparison to a conventional modem startup technique.

[0133] The present invention has been described above with reference to a preferred embodiment. However, those skilled in the art will recognize that changes and modifications may be made to the preferred embodiment without departing from the scope of the present invention. These and other changes or modifications are intended to be included within the scope of the present invention, as expressed in the following claims. 

What is claimed is:
 1. A signaling method for changing operating modes in a data communication system having a first device configured to communicate with a second device via a communication link, said method comprising the steps of: transmitting a modem status signal from said first device to said second device, said modem status signal being configured as a differential phase-shift keying (DPSK) signal based on a predetermined bit pattern; detecting said modem status signal at said second device; and initiating a procedure associated with a change in the operating mode of said data communication system in response to said modem status signal.
 2. A signaling method according to claim 1, wherein said modem status signal represents a modem hold request.
 3. A signaling method according to claim 1, wherein said modem status signal represents a modem hold acknowledgment.
 4. A signaling method according to claim 1, wherein said modem status signal represents a quick reconnect request.
 5. A signaling method according to claim 1, wherein said modem status signal represents a disconnect signal.
 6. A signaling method according to claim 1, wherein said modem status signal is configured as a DPSK signal based on a repetitive sequence of a predetermined bit pattern.
 7. A signaling method according to claim 6, wherein said modem status signal is configured as a DPSK signal based on eight repetitions of a four-bit pattern.
 8. A signaling method according to claim 7, wherein said four-bit pattern is one of the following patterns: 0101, 0011, 0001, or
 0111. 9. A signaling method for changing operating modes in a data communication system having a first device configured to communicate with a second device via a communication link, said method comprising the steps of: receiving a modem status signal in response to a change in the operating mode of said data communication system; detecting said modem status signal by analyzing a number of spectral components associated with said modem status signal; and initiating a procedure associated with said change in the operating mode of said data communication system in response to said modem status signal.
 10. A signaling method according to claim 9, wherein: said modem status signal is configured as a differential phase-shift keying (DPSK) signal based on a predetermined bit pattern; and said detecting step is performed by a tone detector.
 11. A signaling method according to claim 9, wherein: said modem status signal is configured as a differential phase-shift keying (DPSK) signal based on a predetermined bit pattern; and said detecting step is performed by a DPSK receiver.
 12. A signaling method according to claim 9, further comprising the step of receiving an A-tone prior to receiving said modem status signal.
 13. A signaling method according to claim 13, wherein said A-tone is a 2400 Hz tone.
 14. A signaling method for changing operating modes in a data communication system having a first device, resident at a client site, configured to communicate with a second device via a communication link, said method comprising the steps of: receiving, at said first device, an indication related to the termination of an incoming call directed to said client site; transmitting a modem status signal from said first device to said second device, said transmitting step being performed in response to said receiving step; detecting said modem status signal with said second device; and initiating, in response to said detecting step, a quick reconnect procedure to recall a stored operating parameter for said data communication system, said stored operating parameter being associated with a previous communication session between said first and second devices.
 15. A data communication device comprising: a receiver configured to receive a first indication related to an interruption in a current data mode; a transmitter configured to transmit a first modem status signal to a remote data communication device in response to said indication, said first modem status signal being formatted as a differential phase-shift keying (DPSK) signal based on a first predetermined bit pattern; wherein said receiver is further configured to receive a second modem status signal indicative of a modem hold mode, said second modem status signal being formatted as a DPSK signal based on a second predetermined bit pattern.
 16. A data communication device according to claim 15, wherein: said receiver is further configured to receive a second indication related to the termination of an incoming call; said transmitter is further configured to transmit a third modem status signal to said remote data communication device in response to said second indication, said third modem status signal being formatted as a DPSK signal based on a third predetermined bit pattern; and said third modem status signal is formatted to initiate a reconnect procedure to recall a stored operating parameter for said data communication system, said stored operating parameter being associated with a previous communication session conducted by said data communication device. 